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Fuzzer: Add SIMD support to DeNaN #6318

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Feb 21, 2024
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Fuzzer: Add SIMD support to DeNaN #6318

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112 changes: 90 additions & 22 deletions src/passes/DeNaN.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -35,7 +35,7 @@ struct DeNaN : public WalkerPass<
// Adds calls.
bool addsEffects() override { return true; }

Name deNan32, deNan64;
Name deNan32, deNan64, deNan128;

void visitExpression(Expression* expr) {
// If the expression returns a floating-point value, ensure it is not a
Expand Down Expand Up @@ -67,6 +67,13 @@ struct DeNaN : public WalkerPass<
} else {
replacement = builder.makeCall(deNan64, {expr}, Type::f64);
}
} else if (expr->type == Type::v128) {
if (c && hasNaNLane(c)) {
uint8_t zero[16] = {};
replacement = builder.makeConst(Literal(zero));
} else {
replacement = builder.makeCall(deNan128, {expr}, Type::v128);
}
}
if (replacement) {
// We can't do this outside of a function, like in a global initializer,
Expand Down Expand Up @@ -98,6 +105,11 @@ struct DeNaN : public WalkerPass<
i,
builder.makeCall(
deNan64, {builder.makeLocalGet(i, Type::f64)}, Type::f64)));
} else if (func->getLocalType(i) == Type::v128) {
fixes.push_back(builder.makeLocalSet(
i,
builder.makeCall(
deNan128, {builder.makeLocalGet(i, Type::v128)}, Type::v128)));
}
}
if (!fixes.empty()) {
Expand All @@ -115,34 +127,90 @@ struct DeNaN : public WalkerPass<
// Pick names for the helper functions.
deNan32 = Names::getValidFunctionName(*module, "deNan32");
deNan64 = Names::getValidFunctionName(*module, "deNan64");
deNan128 = Names::getValidFunctionName(*module, "deNan128");

ControlFlowWalker<DeNaN, UnifiedExpressionVisitor<DeNaN>>::doWalkModule(
module);

// Add helper functions after the walk, so they are not instrumented.
addFunc(module, deNan32, Type::f32, Literal(float(0)), EqFloat32);
addFunc(module, deNan64, Type::f64, Literal(double(0)), EqFloat64);

if (module->features.hasSIMD()) {
uint8_t zero128[16] = {};
addFunc(module, deNan128, Type::v128, Literal(zero128));
}
}

// Add a de-NaN-ing helper function.
void addFunc(Module* module,
Name name,
Type type,
Literal literal,
std::optional<BinaryOp> op = {}) {
Builder builder(*module);
auto add = [&](Name name, Type type, Literal literal, BinaryOp op) {
auto func = Builder::makeFunction(name, Signature(type, type), {});
// Compare the value to itself to check if it is a NaN, and return 0 if
// so:
auto func = Builder::makeFunction(name, Signature(type, type), {});
// Compare the value to itself to check if it is a NaN, and return 0 if
// so:
//
// (if (result f*)
// (f*.eq
// (local.get $0)
// (local.get $0)
// )
// (local.get $0)
// (f*.const 0)
// )
Expression* condition;
if (type != Type::v128) {
// Generate a simple condition.
assert(op);
condition = builder.makeBinary(
*op, builder.makeLocalGet(0, type), builder.makeLocalGet(0, type));
} else {
assert(!op);
// v128 is trickier as the 128 bits may contain f32s or f64s, and we
// need to check for nans both ways in principle. However, the f32 NaN
// pattern is a superset of f64, since it checks less bits (8 bit
// exponent vs 11), and it is checked in more places (4 32-bit values vs
// 2 64-bit ones), so we can just check that. That is, this reduces to 4
// checks of f32s, but is otherwise the same as a check of a single f32.
//
// (if (result f*)
// (f*.eq
// (local.get $0)
// (local.get $0)
// )
// (local.get $0)
// (f*.const 0)
// )
func->body = builder.makeIf(
builder.makeBinary(
op, builder.makeLocalGet(0, type), builder.makeLocalGet(0, type)),
builder.makeLocalGet(0, type),
builder.makeConst(literal));
module->addFunction(std::move(func));
};
add(deNan32, Type::f32, Literal(float(0)), EqFloat32);
add(deNan64, Type::f64, Literal(double(0)), EqFloat64);
// However there is additional complexity, which is that if we do
// EqVecF32x4 then we get all-1s for each case where we compare equal.
// That itself is a NaN pattern, which means that running this pass
// twice would interfere with itself. To avoid that we'd need a way to
// detect our previous instrumentation and not instrument it, but that
// is tricky (we can't depend on function names etc. while fuzzing).
// Instead, extract the lanes and use f32 checks.
auto getLane = [&](Index index) {
return builder.makeSIMDExtract(
ExtractLaneVecF32x4, builder.makeLocalGet(0, type), index);
};
auto getLaneCheck = [&](Index index) {
return builder.makeBinary(EqFloat32, getLane(index), getLane(index));
};
auto* firstTwo =
builder.makeBinary(AndInt32, getLaneCheck(0), getLaneCheck(1));
auto* lastTwo =
builder.makeBinary(AndInt32, getLaneCheck(2), getLaneCheck(3));
condition = builder.makeBinary(AndInt32, firstTwo, lastTwo);
}
func->body = builder.makeIf(
condition, builder.makeLocalGet(0, type), builder.makeConst(literal));
module->addFunction(std::move(func));
};

// Check if a contant v128 may contain f32 or f64 NaNs.
bool hasNaNLane(Const* c) {
assert(c->type == Type::v128);
auto value = c->value;

// Compute if all f32s are equal to themselves.
auto test32 = value.eqF32x4(value);
test32 = test32.allTrueI32x4();

return !test32.getInteger();
}
};

Expand Down
131 changes: 131 additions & 0 deletions test/lit/passes/denan-simd.wast
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Original file line number Diff line number Diff line change
@@ -0,0 +1,131 @@
;; NOTE: Assertions have been generated by update_lit_checks.py --all-items and should not be edited.

;; RUN: foreach %s %t wasm-opt --denan -all -S -o - | filecheck %s

(module
;; CHECK: (type $0 (func (param v128) (result v128)))

;; CHECK: (type $1 (func (param f32) (result f32)))

;; CHECK: (type $2 (func (param f64) (result f64)))

;; CHECK: (func $foo128 (type $0) (param $x v128) (result v128)
;; CHECK-NEXT: (local.set $x
;; CHECK-NEXT: (call $deNan128
;; CHECK-NEXT: (local.get $x)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (call $deNan128
;; CHECK-NEXT: (v128.const i32x4 0x00000001 0x00000002 0x00000003 0x00000004)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (v128.const i32x4 0x00000000 0x00000000 0x00000000 0x00000000)
;; CHECK-NEXT: )
;; CHECK-NEXT: (drop
;; CHECK-NEXT: (v128.const i32x4 0x00000000 0x00000000 0x00000000 0x00000000)
;; CHECK-NEXT: )
;; CHECK-NEXT: (call $deNan128
;; CHECK-NEXT: (call $foo128
;; CHECK-NEXT: (local.get $x)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
(func $foo128 (param $x v128) (result v128)
;; The incoming param will be de-naned.

;; This is not a NaN. (We do still emit a call for it atm, FIXME)
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Why does this happen?

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No good reason - that's what the code did for f32 and f64 before this PR. I can fix it later.

(drop
(v128.const i32x4 0x00000001 0x00000002 0x00000003 0x00000004)
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It would be useful to write the tests using f32x4 and f64x2 shapes rather than i32x4 so we can better see what values are being passed. You can use the --new-wat-parser and its extensive support for the standard nan formats if you want.

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I was actually thinking it is nice to see the actual bits because of how they are used in the pass (the explanation about the f32 and f64 bits overlapping etc.)?

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To be more specific, in this test code:

    ;; This is an f64 NaN and also an f32. It will become 0's.
    (drop
      (v128.const i32x4 0xffffffff 0x00000002 0x00000003 0x00000004)
    )
    ;; This is an f32 NaN and not an f64. It will also become 0's.
    (drop
      (v128.const i32x4 0x00000001 0xffffffff 0x00000003 0x00000004)
    )

It is nice to see the bits, because that allows the comments to clarify how the same bits can be both f32 and f64 nans, or not.

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I would be more convinced by this if readers were likely to know off the top of their heads what bit patterns correspond to NaNs. I know I don't :)

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Heh, I don't know that either, but I mentioned it in the pass (8 vs 11 top non-sign bits).

)
;; This is an f64 NaN and also an f32. It will become 0's.
(drop
(v128.const i32x4 0xffffffff 0x00000002 0x00000003 0x00000004)
)
;; This is an f32 NaN and not an f64. It will also become 0's.
(drop
(v128.const i32x4 0x00000001 0xffffffff 0x00000003 0x00000004)
)

(call $foo128 (local.get $x))
)
)
;; CHECK: (func $deNan32 (type $1) (param $0 f32) (result f32)
;; CHECK-NEXT: (if (result f32)
;; CHECK-NEXT: (f32.eq
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK-NEXT: (then
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK-NEXT: (else
;; CHECK-NEXT: (f32.const 0)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )

;; CHECK: (func $deNan64 (type $2) (param $0 f64) (result f64)
;; CHECK-NEXT: (if (result f64)
;; CHECK-NEXT: (f64.eq
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK-NEXT: (then
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK-NEXT: (else
;; CHECK-NEXT: (f64.const 0)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )

;; CHECK: (func $deNan128 (type $0) (param $0 v128) (result v128)
;; CHECK-NEXT: (if (result v128)
;; CHECK-NEXT: (i32.and
;; CHECK-NEXT: (i32.and
;; CHECK-NEXT: (f32.eq
;; CHECK-NEXT: (f32x4.extract_lane 0
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK-NEXT: (f32x4.extract_lane 0
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (f32.eq
;; CHECK-NEXT: (f32x4.extract_lane 1
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK-NEXT: (f32x4.extract_lane 1
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (i32.and
;; CHECK-NEXT: (f32.eq
;; CHECK-NEXT: (f32x4.extract_lane 2
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK-NEXT: (f32x4.extract_lane 2
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (f32.eq
;; CHECK-NEXT: (f32x4.extract_lane 3
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK-NEXT: (f32x4.extract_lane 3
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: (then
;; CHECK-NEXT: (local.get $0)
;; CHECK-NEXT: )
;; CHECK-NEXT: (else
;; CHECK-NEXT: (v128.const i32x4 0x00000000 0x00000000 0x00000000 0x00000000)
;; CHECK-NEXT: )
;; CHECK-NEXT: )
;; CHECK-NEXT: )
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